Saoirse Ronan on The Host, ‘Love Squares,’ and Kissing a Smoker

Saoirse Ronan plays not one but two characters in the latest movie adaptation of a Stephenie Meyer novel, The Host: She’s both the human Melanie Stryder and the alien Wanderer (nicknamed Wanda) who has taken up residence in Melanie’s body. (You can always tell when the aliens, who resemble silverfish, have taken over a host because the human’s eyes start to glow in an eerie way.) Intergalactic body-snatching is not without its difficulties, especially in this case, because Melanie refuses to vacate the premises and gets mightily peeved when Wanda starts up a romance with a guy other than the one she already likes. (It’s complicated, and requires lots of making out — just to confirm identity, of course.) Ronan chatted with Vulture about how the kissing scenes went down, how she pranked her co-star, and acting in Ryan Gosling’s directorial debut.

What do you call the geometry of a love triangle when one of the people is really two people? Did you call it a love box?Yes, but I’m not going to say that to the press, now am I? [Laughs.] It sounds a bit sketchy, doesn’t it? You know, Stephenie [Meyer] had a T-shirt made for us that says “Love Box” on it, from American Apparel. I’ve been calling it the “love square,” or the “love parallelogram,” which I like. It’s slanted, on its side, not straight-forward.

How awkward is a love square, then? There’s one scene where you have to kiss two different boys, one right after the other.I mean, that’s certainly not why I was doing the film! [Laughs.] And we’re all mates, so it was just one of those things that we had to do, you know? And it was fine, because we all got along really well. We were always laughing at each other, and we’d had that whenever we did those scenes. Like, Max [Irons] smokes like a trooper. He smokes too much. And he drinks coffee! And Ve Neille — who did the makeup on the film, The Hunger Games, and The Amazing Spider-Man, she’s a legend — she looked after me. Whenever we did the kissing scenes, which was quite frequent, quite often, he’d have five fags in between a shot, and she’d go up to him and be like, “You’re not going near my baby until you take this,” and she’d just hand him a mint. And he said, “What’s that for?” And she said, “Because you stink. So you need to take this.” So she was great.

Did you enlist her for any of the pranks on set?There were a few pranks. To be honest, I can’t remember any of the pranks except this one, so I don’t know how many pranks there were, but … Basically, Max is afraid of things that can fly and bugs. And it was a big mistake to tell us this, because when Jake [Abel] and I heard about it, we’re like, “We’ve got to take advantage of this. We have to find a butterfly or something to put in his trailer.” And he had gone off one day, and I don’t know how we found it, but we found this plastic cockroach. It was on set for some reason. And we decided just as a simple prank to put it in his microwave where we would heat up his lunch every day, and so we put it in. And we were standing far enough away that he couldn’t see us, and he went into his trailer, and literally a few seconds later, he ran out. He was freaking out that this thing was there. But I’m terrible, because I get involved in pranks, but then I get such a kick out of them that I have to tell the person who we’re pranking, because I want them to be involved, too. So I’m like, “Yeah, it’s great, isn’t it, that it’s not a real cockroach?” And he’s like, “What?” So that’s what happened.

How tough was it to wear the glowy-eyes contacts in the desert?It was like lead in my eyes! They’re heavier, see that’s the thing — they’re not just normal contact lenses, they’re a heavier lens. And I was really worried about, because I thought, I’m not going to be able to see anyone through these things! And it was pretty blurry at first. It’s only a little pinhole that you’re looking through. And so I didn’t want to wear them. If I ever look a little uptight onscreen, you know why now. But I had to. If I hadn’t, it would have been 500 grand every minute to put it in digitally. So we had to do it. But it was grand. My eyes adjusted to it, and it was fine.

Stephenie Meyer likes to throw out the rulebook in her fantasy and sci-fi stories. Her Twilight vampires go out in the day, for instance. But you have that in the upcoming Neil Jordan movie Byzantium?We have even more of that, actually. And we don’t even call ourselves vampires. We call ourselves “sucreants.” We don’t have fangs — we have a talon, like a long thumbnail. And so yeah, all the rules were thrown out. What I really liked is that it’s more like folklore, like a legend, like something that’s come out of an old story book. And it’s sad to see these two young women who are floating through whatever era they’re in, can never really settle down, can never really form a relationship with anyone, can never really speak to anyone, because if they tell them, they have to kill them.

You’re about to start shooting with Ryan Gosling for his directorial debut, How to Catch a Monster. What kind of preparation are you doing? Because I would imagine he’s borrowing a page from Derek Cianfrance. We’re shooting in Detroit, so we can’t really stay in the places overnight that we’re going to be in. It’s too dangerous. But we’re certainly going to spend as much time as we can in the locations. Maybe we are going to live together. But we’re not going to have trailers, nothing like that. It’s really very grounded. To be honest, I don’t even like trailers. I prefer to have a little room and to be with everyone else. But to prepare, I’m going to be listening to many different types of music over the next few months, older stuff, sixties stuff, fifties stuff, swing. He’s brilliant, because he’s very open to how the actor feels about the character. We were talking about it the other day, and we were just coming up with really great ideas for the character, and there’s no pressure, really, to stick to a certain type of girl. So we’ll do a lot of preparation when it comes to her look, when it comes to her background, her voice, everything, but really, he’s just going to roll. He’s going to roll and see what happens with a lot of it.